Journal Metrics

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Definitions

Journal Impact Factor:

The Journal Impact Factor is defined as all citations to the journal in the current JCR year to items published in the previous two years, divided by the total number of scholarly items (these comprise articles, reviews, and proceedings papers) published in the journal in the previous two years. Though not a strict mathematical average, the Journal Impact Factor of 1.0 mean that, on average, the articles published one or two years agao have been cited one time. A Journal Impact Factor of 2.5 means that, on average, the articles published one or two years ago have been cited two and a half times. The citing works may be articles published in the same journal. However, most citing works are from different journals, proceedings, or books indexed in Web of Science Core Collection. (Source: Clarivate Analytics)

5-year Journal Impact Factor:

The 5-year journal Impact Factor, available from 2007 onward, is the average number of times articles from the journal published in the past five years have been cited in the JCR year. It is calculated by dividing the number of citations in the JCR year by the total number of articles published in the five previous years. (Source: Clarivate Analytics)

Immediacy index:

The Immediacy Index is the average number of times an article is cited in the year it is published. The journal Immediacy Index indicates how quickly articles in a journal are cited. The aggregate Immediacy Index indicates how quickly articles in a subject category are cited. The Immediacy Index is calculated by dividing the number of citations on articles published in a given year by the number of articles published in that year. Because it is a per-article average, the Immediacy Index tends to discount the advantage of large journals over small ones. However, frequently issued journals may have an advantage because an article published early in the year has a better chance of being cited than one published later in the year. many publications that publish infrequently or late in the year have low Immediacy Indexes. For comparing journals specializing in cutting-edge research, the immediacy index can provide a useful perspective (Source: Clarivate Analytics)

Eigenfactor® Score:

The Eigenfactor Score calculation is based on the number of times articles from the journal published in the past five years have been cited in the JCR year, but it also considers which journals have contributed these citations so that highly cited journals will influence the network more than lesser cited journals. References from one article in a journal to another article from the same journal are removed, so that Eigenfactor Scores are not influenced by journal self-citation. (Source: Clarivate Analytics)

Article Influence Score:

The Article Influence Score determines the average influence of a journal's articles over the first five years after publication. It is calculated by multiplying the Eigenfactor Score by 0.01 and dividing by the number of articles in the journal, normalized as a fraction of all articles in all publications. This measure is roughly analogous to the 5-Year Journal Impact Factor in that it is a ratio of a journal's citation influence to the size of the journal's article contribution over a period of five years. (Source: Clarivate Analytics)

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Editorials and other content

• Nature and the Nature journals are diversifying their presentation of performance indicators. Nature. Time to remodel the journal impact factor, July 2016
• The journal impact factor is a much-criticized yet still-used number. As with any metric, it should not be used uncritically and without an understanding of what it measures. Nature Methods. On Impact, August 2015.
• Use these ten principles to guide research evaluation, urge Diana Hicks, Paul Wouters and colleagues. Nature. Bibliometrics: The Leiden Manifesto for research metrics, 22 April 2015.
• The San Francisco Declaration on Research Assessment (DORA), an initiative spearheaded by the American Society for Cell Biology, aims to reform research assessment. Nature Cell Biology. Ending the tyranny of the impact factor, January 2014.
• In deciding how to judge the impact of research, evaluators must take into account the effects of emphasizing particular measures — and be open about their methods. Nature. The maze of impact metrics, 17 October 2013.
• As the journal's first impact factor is released, it is time to reflect on journal metrics and how Nature Climate Change has been making its mark. Nature Climate Change. Having an impact, July 2013.
• Citation analyses can condense scholarly output into numbers, but they do not live up to peer review in the evaluation of scientists. Online usage statistics and commenting could soon enable a more refined assessment of scientific impact. Nature Materials. Measuring impact, July 2011.
• The classic impact factor is outmoded. Is there an alternative for assessing both a researcher's productivity and a journal's quality? Nature Immunology. Ball and chain, October 2010.
• Nature Metrics special, June 2010. The value of scientific output is often measured, to rank one nation against another, allocate funds between universities, or even grant or deny tenure. Scientometricians have devised a multitude of 'metrics' to help in these rankings. Do they work? Are they fair? Are they over-used? Nature investigates.
• Transparency, education and communication are key to ensuring that appropriate metrics are used to measure individual scientific achievement. Nature. Assessing Assessment, 17 June 2010.
• Research assessment rests too heavily on the inflated status of the impact factor. Nature. Not-so-deep impact, 23 June 2005.

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